Lecture 14
October 1, 2004
Review of Static Electric Fields – II
Conductors in Static Electric Field
Inside a Conductor 
Boundary Conditions at a Conductor/Free space
Interface:
Et = 0 and 
.
Dielectrics in Static Electric Field
where equivalent charge densities
Electric Flux density: 
Gauss’s law: 
Linear and isotropic medium: 
where 
is electric susceptivility.
Boundary Conditions: E1t=E2t (V/m), and D1n - D2n
= rs (C/m^2)
Capacitance: 
Parallel-plate capacitor: 
Cylindrical Capacitor: 
Spherical capacitor: 
Electrostatic Energy
Electrostatic Energy needed to assemble a N charge
system:
Electrostatic Energy in terms of Field Quantities: 
Capacitance in terms of electrostatic field energy: 
.
Electrostatic Forces
System with fixed charges:
.
System with fixed potentials: 